COLLEGE OF SCIENCE,ZHEJIANG UNIVERSITY
A Toy Model for the Pseudogap Phase in Cuprate Superconductors
Dr. Kun Yang
National High Magnetic Field Lab,
(light refreshments will be served prior to the
In this talk I discuss a simple model we introduced that have a number of
features qualitatively similar to the phenomenology of Cuprate superconductors, especially the existence of a pseudogap region in the phase diagram. In this
model Cooper pairing is induced by an attractive interaction with a finite range. While returning to the usual BCS limit when the range of the pairing
interaction L is shorter than the mean-field coherence length \xi, the physics becomes qualitatively different from that of BCS when L is much larger than
\xi. In this regime the system supports a new class of low-energy collective modes absent in the BCS theory,
whose fluctuations greatly depress the superconducting transition temperature (Tc) from its mean-field level, and
lead to pseudogap behavior above Tc. These fluctuations are not the usual phase fluctuations of the standard superconducting order parameter, and lead
to a highly unusual Ginzburg-Landau description in which the center of mass and relative degrees of freedom of the order parameter must be included on
equal footing. I will discuss how such a long-range pairing interaction may
arise in Cuprate superconductors, especially in the underdoped regime.
 Kun Yang and S. L. Sondhi, Phys. Rev. B 62, 11778 (2000).